I had the same problem. Within 48 hours of owning (less than that) my truck heated up almost all the way over so I shut off the A/C and pulled over. Fans were blaring and I noticed the temp went down so I kept it running. I checked and my coolant reservoir was completely empty.
Went to the dealer and they filled and pressure tested, found nothing wrong and informed me there was air that finally worked its way out (brand new truck, so nearly no miles on it).
1 week later was cleaning leaves off windshield and popped the hood to remove some more. For the heck of it checked coolant again - empty entirely again. I brought it right to the dealer where it remained for 6 days until today. They tested everything and were in continuous contact with STAR.
Leak down test, compression test, looked into every cylinder with a scope. Replaced radiator cap, checked oil, transmission fluid, inside cabin, under hood everywhere. Nothing. After another cooling system pressure test and them driving my truck for 55 miles by the time I got it back, they again said the same thing - air in system purged its way out, lowering the level. I have the full STAR-mechanic transcripts of their correspondence with my receipt.
That's the second time bringing my brand new truck that I had for 2 weeks in for this issue. I will continue to monitor it and if it is empty again I will open up my own case with STAR, get a case number and bring it right back to the dealer.
I spoke with the OP of this thread and he was kind enough to respond. He said his leak was due to a bad transmission cooler which was replaced and it is fine now. My issue has been frustrating but I want any other poor souls who are trying to enjoy their new truck to have some information to work off of. I will post more in the future here if anything else happens with this.